1. Field of the Invention
The present invention relates to the field of light microscopy. More specifically, this invention relates to multi-axis imaging systems, particularly an array of miniature imaging systems which can scan an entire specimen on a microscope slide in a single pass.
2. Discussion of the Background
Pathologists are physicians responsible for analyzing tissue specimens, fine-needle aspirates of tissues, cytology specimens, and liquid specimens such as urine or blood by light microscopy. Analysis of specimens frequently is accomplished by viewing specimens on slides through a light microscope or by viewing electronic images of the specimens on a video monitor. Video images can be obtained by mounting a video camera on a conventional light microscope and capturing images in either an analog or digital imaging mode. Microscopes with motorized stages translate slides to move one portion of the specimen on the slide into a field of view of the microscope and then translate to move another portion of the specimen into the field of view. Microscopic digital images of entire specimens can be assembled from the individual digital images.
Light microscopes have a field of view (FOV) measuring from tens of microns to millimeters in diameter, depending on the transverse magnification of the microscope objective. To image an entire standard microscope slide (i.e., a 25 mm by 75 mm microscope-slide) requires a conventional light microscope to scan back and forth multiple times. The scanning process is time intensive. As a result, ordinarily not all portions of the pathological specimen are imaged. Rather, the pathologist depends on statistics to determine a normal or an abnormal culture. Digital images of a percentage of the pathological specimen are scanned and captured in a matter of minutes using the conventional motorized light microscope.
While it is possible to design an optical system with a single optical pathway which has a FOV comparable to the microscope slide width, this design requires a very large objective lens which in turn produces a large imaging system requiring substantial stabilization of the microscope during scanning and imaging. As a result, microscopes with smaller objectives and smaller FOVs have been used, and a subsample of a few thousand fields of the pathological sample may be relied upon to represent the histopathology, cytopathology, or histomorphology of the specimen. The complete pathological sample is not necessarily viewed, which can be suboptimal for medical purposes.
Related U.S. Patent Application Ser. No. 60/276,498 entitled MINIATURZED MICROSCOPE ARRAY AND DIGITAL SLIDE SCANNER discloses a novel method and apparatus for rapidly obtaining an image of an entire slide using an array microscope. In general, this is a multiple-optical-axis, or multi-axis, imaging system having a plurality of imaging elements arranged in an array, each imaging element having one or more optical elements disposed along the optical axis thereof. Where the imaging elements are microscopes, the system is a microscope array (MA), or miniature microscope array (MMA) since the imaging elements are preferably very small. Where used to image a single object, the system may be referred to as an “array microscope”.
In a multi-axis imaging system such as an MMA, where the imaging elements are closely packed, cross talk between the plurality of imaging elements at the image sensors is a serious problem. Cross talk is caused by unwanted light that originates outside the field of view of an individual imaging element. The field of view is defined herein as the projection of an image-plane sensor or a segment of an image-plane sensor associated with the individual imaging system into an object space, e.g., into an object plane that is conjugate to the image plane. Failure to suppress cross talk in a multi-optical-axis imaging system can lead to a reduction of contrast and/or a reduction in image quality in an image. While the term “cross talk” includes light from neighboring imaging elements, as used herein it is not limited thereto.
As described in the Summary of the Invention and Detailed Description of the Preferred Embodiment hereafter, the present invention is directed to a multi-axis imaging system. In such a system, an individual imaging element can be thought of as being surrounded not by an opaque housing, as is the typical configuration for a single-optical-axis imaging system, but instead by a light-transmitting structure that consists of the neighboring imaging elements and the support structure associated with the multi-axis imaging system. As a result and because of close packing of the imaging elements, light from one imaging element can propagate into another neighboring imaging element; the many surfaces needed to produce multi-axis imaging systems can lead to numerous reflections and scattering of light; and the use of transparent substrates for the arrays of optical elements can allow light to propagate outside an optical element's aperture and yet reach an image sensor.
Accordingly, it can be appreciated that there is a particular need in a multi-axis imaging system to reduce cross talk between imaging elements and other undesirable effects due to unwanted light that reduce image contrast and image quality.